create table
USERS( id number constraints PK_USER PRIMARY KEY,
NAME NVARCHAR2(50) constraints UQ_USER_NAME UNIQUE NOT NULL,
AGE NUMBER CHECK(AGE>0),
BIRTHDATE DATE
);


create sequence SEQ_USERS;

INSERT into users(id,name,age,birthdate) values(seq_users.nextval,'jack_ma',55,sysdate);

update users set age=1 where id=2;

delete from users where id=1;



select * from users;

commit;